We, the present inventors, recently discovered that a substance active against esterase is present in the culture as obtained by cultivating a microorganism which was isolated from a soil sample collected in the ground of Biseibutsu Kagaku Kenkyu-sho in Shinagawa-ku, Tokyo, Japan and which was designated Streptomyces MD4-Cl. We succeeded in isolating this substance from said culture. As a result of investigation, this substance is found to be a new substance and now named esterastin. We have made extensive research on whether esterastin is useful as a medicine for any purpose. In consequence, we have now found that esterastin is active to reduce the number of the cells forming humoral antibody and also to suppress the cellular immunity. As esterastin is a substance of a very low toxicity, this substance is a physiologically active compound which may be used with safety as a drug to treat diseases caused by the immune reactions such as, for example, contact allergic dermatitis, systemic lupus erythematosus, autoimmune hemolytic anemia, periarteritis nodosa, myasthenia gravis, arthritis, rheumatism and multiple sclerosis and which may be used as an immunosuppressive drug in the surgical operations of transplantation of an internal organ such as heart, kidney and muscle. Esterastin is also expected to be useful as an anti-inflammatory agent because it inhibits the activation of the complement system owing to its esterase-inhibiting activity.
We made systematic research to seek for a physiologically active substance which is inhibitory to the decomposition of p-nitrophenyl acetate by esterase, and during this research we discovered esterastin in the fermentation broth of the above-mentioned microorganism as stated hereinbefore.
Further investigation of esterastin reveals that this substance has the chemical structure shown below.